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LENS BASICS

Lens terminologies

Circular aperture

In general, if an aperture uses 7, 9 or 11 aperture blades, then the shape of the aperture becomes a 7-sided, 9-sided or 11-sided polygon as the aperture is made smaller. However, this has a certain undesirable effect in that the defocusing of point light sources appears polygonal and not circular. α lenses overcome this problem through a unique design that keeps the aperture almost perfectly circular from its wide-open setting to when it is closed by 2 stops. Smoother, more natural defocusing can be obtained as a result.

Extra-low Dispersion (ED) glass / Super ED glass

As focal lengths get longer, lenses built with conventional optical glass have difficulties with chromatic aberration, and as a result images suffer from lower contrast, lower color quality, and lower resolution. To counter such problems, ED glass was developed and is included in select lenses. It dramatically improves chromatic aberration at telephoto ranges, and provides superior contrast across the entire image, even at large aperture settings. Super ED glass provides enhanced compensation for chromatic aberration.

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[1] Glass [2] ED glass [3] Super ED glass [4] Focal plane

Multi-layered coating

Although most of the light that falls on an optical glass transmits right through, some of it reflects at the surface of the lens to cause flare or ghost images. In order to avoid this problem, a thin layer of anti-reflective coating must be applied to the lens surface. α lenses use exclusive multi-layered coating to effectively suppress such problems over a wide spectrum of wavelengths.

Nano AR Coating

Original Sony Nano AR Coating technology produces a lens coating that features a precisely defined regular nano-structure that allows accurate light transmission while effectively suppressing reflections that can cause flare and ghosting. The reflection suppression characteristics of the Nano AR Coating are superior to conventional anti-reflective coatings, including coatings that use an irregular nano-structure, providing a notable improvement in clarity, contrast, and overall image quality.

Aspherical lens

Spherical aberration is a slight misalignment of light rays projected on the image plane by a simple spherical lens, caused by differences in refraction at different points on the lens. That misalignment can degrade image quality in large-aperture lenses. The solution is to use one or more specially shaped “aspherical” elements near the diaphragm to restore alignment at the image plane, maintaining high sharpness and contrast even at maximum aperture. Aspherical elements can also be used at other points in the optical path to reduce distortion. Well designed aspherical elements can reduce the total number of elements required, thus reducing overall lens size and weight.

[1] Spherical lens [2] Aspherical lens [3] Focal plane

Advanced Aspherical

Advanced Aspherical (AA) elements are an evolved variant, featuring an extremely high thickness ratio between the center and periphery. AA elements are exceedingly difficult to produce, depending on the most advanced molding technology available to consistently and precisely achieve the required shape and surface accuracy. The result is significantly improved reproduction and rendering.

XA (extreme aspherical) lens

Aspherical lenses are much more difficult to manufacture than simple spherical types. New XA (extreme aspherical) lens elements achieve extremely high surface precision that is kept to within 0.01 micron by innovative manufacturing technology, for an unprecedented combination of high resolution and the most beautiful bokeh you’ve ever seen.

ZEISS® T* Coating

The fact that lens coating technology – vapor deposition of a thin, even coating on the lens surface to reduce reflections and maximize transmission – was originally a ZEISS patent is well known. The ZEISS company also developed and proved the efficacy of multi-layer coatings for photographic lenses, and this is the technology that became the T* coating.

Until the introduction of coated lenses, the lens surface would reflect a large percentage of the incoming light, thus reducing transmission and making it difficult to use multiple of elements in lens designs. Effective coatings made it possible to design more complex optics that delivered significantly improved performance. Reduced internal reflection contributed to minimum flare and high contrast.

The ZEISS T* coating is not simply applied to any lens. The T* symbol only appears on multi-element lenses in which the required performance has been achieved throughout the entire optical path, and it is therefore a guarantee of the highest quality.

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[1] Light source [2] Image sensor [3] Reduced reflection

Internal focusing (IF)

Only the middle groups of the optical system are moved to achieve focusing, which leaves the total length of the lens intact. Benefits include fast autofocusing and a short minimum focusing distance. Also, the filter thread at the front of the lens does not rotate, which is convenient if you’re using a polarizing filter.

Rear focusing (RF)

By moving only the rear group of lenses to focus, the lens allows for speedy AF operation and a shorter minimum focusing distance. Also, because the front of the lens does not rotate, operability is improved when you’re shooting with a polarizing filter attached.

Aluminum alloy lens barrel

Aluminum alloy is used in the construction of the G Lenses and other high-end lenses to ensure high optical performance. This material is lightweight, durable, and highly resistant to the effects of temperature change.

Focus range limiter (FRL)

This function saves you a bit of time during AF operation by setting a limit on the focusing range. In macro lenses, this limit can be on either the near or far range (as pictured). In the SAL70200G, the limit is set on far ranges only. In the SAL300F28G, focusing can be limited either to a far range or to a range that you specify yourself.

Focus hold button (FHB)

Once you’ve adjusted focus to where you want it, pressing this button on the lens barrel will keep the lens locked to that focusing distance. The preview function can also be assigned to this button through the camera’s custom settings.

Direct Drive Super Sonic wave Motor (DDSSM)

A new DDSSM system is used for precision positioning of the heavy focus group required for the full-frame format, allowing precision focusing even within the lens’s shallowest depth of field. The DDSSM drive system is also remarkably quiet, making it ideal for shooting movies where focus is constantly changing while the scene is being recorded.

Super Sonicwave Motor (SSM)

SSM is a piezoelectric motor that contributes to smooth and silent AF operation. The motor produces high torque at slow rotation, and provides immediate start and stop responses. It is also extremely quiet, which helps keep autofocusing silent. Lenses that feature SSM also include a position-sensitive detector to directly detect the amount of lens rotation, a factor that improves AF precision overall.

SSM consists of a rotor (left) and a stator (right) on which piexoelectric elements are mounted.

ADI flash metering

Advanced Distance Integration flash metering is available when the built-in flash, or HVL-F60M / HVL-F43M / HVL-F20M external flash is used together with a lens that has a built-in distance encoder.* It provides automatic metering that is virtually unaffected by the reflectance of subjects or backgrounds. Precise distance information is obtained through the encoder, and this data is used to compensate the flash output accordingly. This yields good exposures more reliably than conventional TTL (through-the-lens) flash metering, which can be thrown off by overly reflective or overly dark subjects and background.

Distance encoder

The distance encoder is a lens component that directly detects the position of the focusing mechanism, and sends a signal to the CPU in order to measure distance to the subject. During flash photography, this data is very useful in calculating how much flash output is appropriate to the scene. The distance encoder plays an integral part in ADI flash metering, which delivers high precision flash metering that is unaffected by the reflectance of subjects or backgrounds.

Smooth Autofocus Motor (SAM)

Rather than using the focus drive motor in the camera body, SAM lenses feature an autofocus motor built into to the lens itself that directly drives the focusing element group. Since the built-in motor directly rotates the focus mechanism, operation is significantly smoother and quieter than conventional coupled autofocus drive systems.

Lens-based optical image stabilisation (OSS)

Gyro sensors built into the lens detect even the slightest movement, and the stabilization lens is precisely shifted to counteract any image blur that might occur. The use of precision, quiet linear motors and technology inherited from high-end Sony professional camcorders results in exceptionally quiet, effective image stabilization that contributes to high-quality movies as well as stills.

Active Mode (Active Mode OSS)

Moving around while shooting movies means more camera shake that can cause blur. Although conventional image stabilization systems were not effective at compensating for this type of movement, “Active Mode” employs a wider range of motion for the compensation lens, achieving improved stabilization over a greater range of camera movement. Stabilization at the wide end of the zoom range is significantly improved, facilitating handheld movie shooting with minimum image blur.

Fluent, flexible power zoom (PZ)

Sony α mount lenses that feature power zoom offer enhanced control and expressive potential for moviemaking, with smooth, consistent zooming that is difficult to achieve manually. Details like smooth acceleration and deceleration are important too, and of course tracking is excellent throughout. All of this is made possible by a blend of mature Sony's camcorder technology with state-of-the-art innovation, from optical and mechanical design to original Sony's actuator technology that all comes together through exacting in-house manufacturing. Internal zoom is another beneficial feature: the length of the lens remains constant while zooming, and the barrel does not rotate so polarizers and other position-dependent filters can be used without the need for additional support.

Smooth Motion Optics (SMO)

SMO (Smooth Motion Optics) is a Sony optical design concept for interchangeable lenses that is specifically aimed at achieving the highest possible image quality and resolution for motion images.

SMO design addresses three main issues that are critical for moviemaking:

- Small focus shifts that can occur while zooming are eliminated by a special tracking adjustment mechanism.

- Lateral movement of the optical axis while zooming is eliminated by an internal zoom mechanism that keeps the length of the lens constant at all focal lengths.

The level of precision required demands both exacting design and constant monitoring during manufacture, but the benefits for moviemaking with large aperture lenses, particularly on large format sensors, are spectacular and well worth the effort.